To troubleshoot this, first reupload all the original vB non-image files (except install.php). Make sure you upload these in ASCII format and overwrite the ones on the server. Also be sure to upload the admincp files to whichever directory you have set in your config.php file. Then run 'Suspect File Versions' in Diagnostics to make sure you have all the original files for your version and that none show 'File does not contain expected contents':
Admin CP -> Maintenance -> Diagnostics -> Suspect File Versions

[Note: In some cases you may also need to remove any of the listed .xml files in the includes/xml directory.]

Next, disable all plugins.

Note: To temporarily disable the plugin system, edit config.php and add this line right under <?php

define('DISABLE_HOOKS', true);

Then if you still have this problem, create a new style and choose no parent style. This will force it to use the default templates. Finally empty your browser cache, close all browser windows then try again. Make sure you change to the new style and view your forums with it. Do you have the same problem?

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obviously some of the above will not apply to you, but that is the general first thing you do. Check your plugins and hacks you have done to your board!

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2nd, you said your database was compromised a few months ago or something. Well that rings alarm bells straight away.
Provide more info on this aspect and it may shed some light.

This will help with the script kiddies - and XSS and system injection attacks - if your server or site was compromised it was because the security sucked.

Also I would make sure you have cpanel server locked down - go to the cpanel forums to find out how.

Do you have shell access to the server?

You may want to run rkhunter and see whats up.

If you have been comprimised for a month - well best advice to you is - redo the server - i.e. wipe it clean and reinstall the OS lock it down, install mod security and trip wire - rebuild your forum etc and go from there.

A system that has been hacked for a month is screwed no matter what you do.